The study is an intraindividual comparison of two methods. The number of subjects to be enrolled is 47 patients. All participants will receive both two treatments in a single visit : a first period of 2.5 hours of illumination with FLEXITHERALIGHT device followed by a continuous red light Spectrum (between 7 and 10 minutes) with Aktilite® after an appropriate incubation of methyl aminolevulinate).